360 
may, perhaps, appear imperfect to those accustomed to the 
study of the spectra of substances in the state of incandescence, 
but it is in all respects well adapted for the study of the 
spectra of solutions, in which a slight difference in the cha- 
racter of the solvent often makes far more difference in the 
position of the bands than any that could result from errors 
due to the employment of such a scale and notation. To 
hold the liquids under examination, I in most cases employ 
narrow, deep cells, usually one eighth of an inch diameter, 
and half an inch deep, so mounted that they can be examined 
either in the line of the length or at the side ; but occasion- 
ally I use rather wider, as much as two and a half inches 
long. 
By using these narrow cells very much less material is 
required for successful examination, which is not only most 
important when very little is at command, but even in other 
cases often effects a considerable saving of time in filtration 
and evaporation. 
1 shall divide my subject into three principal heads, viz. : 
1. Various facts connected Avith Avine; 2. Those relating to 
malt liquors ; and — 3. Such as illustrate the methods that 
may be employed to detect adulteration in various substances 
used as food or medicine. 
1. On the Colouring Matters of T Vines. 
The pure colour of fresh dark grapes is best prepared by 
removing the skins, heating them in alcohol, evaporating 
the solution to dryness, redissolving it in a little Avater, 
filtering, and again evaporating to dryness in a small saucer, 
in Avhich the colour may be kept as a stiff syrup for many 
months Avithout material change. It belongs to the group 
of colours which I called group B in my paper in the ‘ Pro- 
ceedings of the Royal Society ’ — that is to say, sulphite of 
soda produces no immediate effect when added to a solution 
rendered alkaline by ammonia ; but when added to one 
made acid with citric acid, it almost immediately removes 
the detached absorption in the green, so that the solution 
becomes very pale. 
Since this colour of dark grapes is purple Avhen dry and 
quite neutral, it may be called Vitis purple. I have not yet 
met Avith it in any other fruit, unless it be in that of the 
common croAvberry ( Empetrum nigrum). One of its pecu- 
liarities is that it easily passes into insoluble modifications. 
It belongs to my sub-group B al 0 am 0 , since it does not give 
any decided narroAV absorption band in an alcoholic solution, 
AA r hen either neutral or with excess of ammonia. Such 
